Biological Rhythms

• What are biological rhythms?

  Cyclical changes in biological systems
• Why do organisms have biological rhythms?

  To optimize behavior in their environment
• What is the most important biological rhythm for humans?

  Circadian rhythm
• How long does a circadian rhythm last?

  24 hours
• What does a circadian rhythm optimize in organisms?

  Physiology and behavior for day-night cycles
• What is the master circadian pacemaker in humans?

  Suprachiasmatic nuclei (SCN)
• Where is the SCN located?

  In the hypothalamus
• What is photoentrainment?

  Alignment of circadian rhythm with light
• How do light-sensitive cells in the eye affect circadian rhythms?

  They send light level messages to the SCN
• What regulates the sleep/wake cycle?

  Circadian rhythm
• When do people typically feel the strongest need to sleep?

  Between 2:00 and 4:00 a.m.
• What is the post-lunch dip?

  Sleepiness between 1:00 and 3:00 p.m.
• How does sufficient sleep affect sleepiness during dips?

  It makes sleepiness less intense
• What is homeostatic control in relation to sleep?

  It increases sleep drive with prolonged wakefulness
• When does the homeostatic drive for sleep reach its maximum?

  In the late evening
• What happens to the internal circadian clock in the absence of external cues?

  It maintains a cycle of 24 or 25 hours
• How does shift work affect the circadian system?

  It causes misalignment of the biological clock
• What is the lowest core body temperature during a circadian rhythm?

  About 36 degrees Celsius
• When does core body temperature peak?

  About 38 degrees Celsius at 6 p.m.
• What role does melatonin play in sleep?

  Encourages feelings of sleep during darkness
• When are peak levels of melatonin produced?

  During the hours of darkness
• What are the strengths and weaknesses of research into circadian rhythms?

  Strengths:

  • Real-life applications in chrono therapeutics
  • Improved treatment timing for medications

  
  

  Weaknesses:

  • Case study limitations
  • Small sample sizes affecting generalizability
• Who is Michel Siffre?

  A French cave explorer studying circadian rhythms
• What did Michel Siffre's studies reveal about circadian rhythms?

  They settled around 24 to 25 hours
• What is a limitation of case studies in circadian rhythm research?

  They often involve small sample sizes
• How did Siffre's age affect his internal body clock?

  It slowed down as he aged
• What is the longest biological rhythm mentioned?

  Infradian rhythm
• What is the duration of an infradian rhythm?

  Longer than 24 hours
• What is the duration of an ultradian rhythm?

  Less than 24 hours
• What is a cyclical pattern within biological systems called?

  Biological rhythm
• What regulates the female menstrual cycle?

  Hormones
• What is the longest biological rhythm mentioned?

  Infradian rhythm
• What is the duration of an infradian rhythm?

  Longer than 24 hours
• When does ovulation typically occur in the menstrual cycle?

  Roughly halfway through the cycle
• What is the duration of an ultradian rhythm?

  Less than 24 hours
• What hormone levels are highest during ovulation?

  Estrogen levels
• What is a circadian rhythm approximately equal to?

  24 hours
• What are biological rhythms?

  Cyclical patterns within biological systems
• What happens to progesterone levels after ovulation?

  They increase
• What is the typical duration of a menstrual cycle?

  Around 28 days